Lecture 03/03

Question 1

Explain equilibrium cooling

Answer 1

• Very slow cooling
• Uniform % composition through the structure
• Equilibrium structure

Question 2

Explain non-equilibrium cooling

Answer 2

• Rapid cooling
• Diffusion is time-dependent
• Diffusion in solid is slower than that in liquid and at lower temps
• Microstructure shows different % compositions as the liquid cools with higher concentration in the middle
• Cored structure

Question 3

The displacement of the non-equilibrium solidus curve depends on? What is the relationship?

Answer 3

Rate of cooling, slower the cooling rate, smaller displacement

Question 4

What is segregation?

Answer 4

Concentration gradients are established across the grains

Question 5

How can coring be eliminated?

Answer 5

Homogenization heat treatment

Question 6

What happens when a cored structure is reheated?

Answer 6

The grain boundaries will melt first, resulting in a sudden loss in mechanical integrity

Question 7

Describe the tensile strength and ductility for isomorphous alloys

Answer 7

• TS will go up with the addition of a second component

- Ductility will go down

Question 8

What is the eutectic point?

Answer 8

Point when you go directly from liquid to solid

Question 9

How many single phase regions in a binary eutectic system?

Answer 9

3

Question 10

Explain a phase diagram of a binary eutectic system

Answer 10

• Points B and G, maximum solubility
• Line ABC, HGF, solubility limit
• 3 two phase regions
• 3 single phase regions
• Point E, eutectic point
• BEG line, lowest temp at which liq. phase may exist, eutectic isotherm

Question 11

What is the eutectic reaction?

Answer 11

On cooling, a liquid becomes 2 solid phases at the same time

Question 12

The eutectic forms in?

Answer 12

Alternating layers

Question 13

Explain primary and eutectic phase

Answer 13

Primary phase is formed in the alpha +L phase, eutectic is formed upon crossing the eutectic isotherm

Question 14

What is a microconstituent?

Answer 14

Element of the microstructure having an identifiable and characteristic structure

Question 15

What are terminal solid solutions?

Answer 15

2 solid phases near the extremes of composition

Question 16

What are intermediate phases?

Answer 16

Phases between the terminal phases

Question 17

What are intermetallic compounds?

Answer 17

Metal-metal systems with distinct chemical formulas

Question 18

What is the eutectoid reaction?

Answer 18

One solid phase becomes 2 solid phases

Question 19

What is the peritectic reaction?

Answer 19

1 solid + Liquid becomes a solid

Question 20

What are congruent transformations?

Answer 20

No compositional alterations occur

Question 21

What are incongruent transformations?

Answer 21

At least one phase experiences a change in composition

Question 22

What is the Gibbs phase rule?

Answer 22

How many phases that coexist within a system at equilibrium

Question 23

What is the general form of the Gibbs phase rule?

Answer 23

P+F = C+N 
P - phases present
F - degrees of freedom
C - components in the system
N - non-composition variables

Question 24

Where is the condition met for 0 degrees of freedom?

Answer 24

Eutectic point, 3 phases are present